1. Field of the Invention
The present invention relates to a Code Division Multiple Access (CDMA) type demodulator device. In particular, the present invention relates to a technique for demodulating information carried by respective channel signals from an up link signal specified in the CDMA standard conforming to IS-2000.
2. Description of the Related Art
FIG. 2 is a circuit diagram showing an exemplary structure of a modulator device 10. The modulator device 10 is installed in a transmitter conforming to the current standard, i.e., the standard in conformity to IS-2000. The standard in conformity to IS-2000 is a standard which may be applied to CDMA receivers or cellular telecommunication systems according to CDMA modulation/demodulation techniques. The up link signal according to the standard in conformity to IS-2000 is composed of three channel signals, that is, a pilot channel signal, a supplemental channel signal and a fundamental channel signal.
In the circuit arrangement shown in FIG. 2, the modulator device 10 processes information for the pilot channel signal, information for the supplemental channel signal and information for the fundamental channel signal. The modulator device 10 includes multipliers A1 and A2, gain adjustment circuits A3 and A4, an adder A5, multipliers A6, A7, A8, A9, A10 and A11, adders A12 and A13, filter circuits A14 and A15 and an adder A16.
The multiplier A1 modulates the information for the supplemental signal with the first Walsh-Code sequence. Such a modulation is generally called as spread spectrum modulation. As a result of the modulation using the first Walsh-Code sequence, the supplemental channel signal is obtained.
The multiplier A2 modulates the information for the fundamental signal with the second Walsh-Code sequence, thereby the fundamental channel signal is obtained.
The gain adjustment circuits A3 and A4 adjust a gain of an amplitude component of the supplemental channel signal and a gain of an amplitude component of the fundamental channel signals, respectively.
The adder A5 multiplexes the supplemental channel signal output from the gain adjustment circuit A3 and the fundamental channel signal output from the gain adjustment circuit A4, so as to obtain an information channel signal.
The multiplier A6 multiplies a long-code sequence, that is a part of a PN(Pseudorandom Noise)-Code sequence, by a PN (Pseudorandom Noise)-Code sequence that corresponds to an inphase component, PNi, thereby the first orthogonal code sequence is obtained. Similarly, the multiplier A7 multiplies the above long-code sequence by a PN (Pseudorandom Noise)-Code sequence corresponding to a quadrature component, PNq, thereby the second orthogonal code sequence.
The multiplier A8 modulates the pilot channel signal carrying the information for the pilot channel signal by spread spectrum modulation using the first orthogonal code sequence output from the multiplier A6. The modulated pilot channel signal is used as an inphase component of the pilot channel signal. The multiplier A9 modulates the information channel signal output from the adder A5 by spread spectrum modulation using the first orthogonal code sequence output from the multiplier A6. The modulated information channel signal is used as a quadrature component of the information channel signal. The multiplier A10 modulates the information channel signal from the adder A5 by spread spectrum modulation using the second orthogonal code sequence output from the multiplier A7. The thus modulated information channel signal is used as an inphase component of the information channel signal. The multiplier A11 modulates the pilot channel signal with spread spectrum modulation using the second orthogonal code sequence output from the multiplier A7. The thus modulated pilot channel signal is used as a quadrature component of the pilot channel signal.
The adder A12 multiplexes the inphase component of the pilot channel signal output from the multiplier A8 and that of the information channel signal output from the multiplier A10, thereby an inphase component of a channel signal is obtained. The adder A13 multiplies the quadrature component of the pilot channel signal output from the multiplier A9 and the quadrature component of the information channel signal from the multiplier. The multiplexed signal is used as a quadrature component of the channel signal.
The filter circuit A14 adjusts the gain of the amplitude component of the inphase component of the channel signal output from the adder A12 by a low-pass filter. The filter circuit A14 rotates the phase of the adjusted signal by 90 degrees. The resultant signal is used as an inphase component of a transmitted signal TS. The filter circuit A15 adjusts the gain of the quadrature component of the channel signal output from the adder A13 by a low-pass filter. The thus adjusted signal is used as a quadrature component of the transmitted signal TS.
The adder A16 multiplexes the inphase and the quadrature components of the transmitted signal TS that are respectively output from the filter circuits A14 and A15, so as to obtain the transmitted signal TS.
As described above, the modulator device 10 modulates information for the three channel signals, i.e., information for the pilot channel signal, information for the supplemental channel signal and information for the fundamental channel signal by spread spectrum modulation using Walsh-Code sequence or spread spectrum modulation both Walsh-Code sequence and Orthogonal-Code sequence. The modulator device 10 multiplexes the modulated three channel signals to obtain the transmitted signal TS, and then transmits the transmitted signal TS.
It should be noted that the pilot channel signal is different from the supplemental channel signal that is used as the information channel signal. Also, the pilot channel signal is different from the fundamental channel signal that is used as the information channel signal. The modulator device 10 does not modulate the pilot channel signal by the spread spectrum modulation using the Walsh-Code sequence. Instead, the pilot channel signal is used for estimating a radio propagation path. When the receiver demodulates the pilot channel signal, the receiver uses a demodulation method different from that used for the supplemental channel signal and the fundamental channel signal.
FIG. 3 shows an exemplary demodulator device 11 included in the receiver. The demodulator device 11 receives the transmitted signal TS transmitted from the transmitter having the modulator device 10 as a received signal RS. The received signal RS is a signal that has passed through a propagation path composed of a multi-path fading environment. The demodulator device 11 extracts the three channel signals, i.e., the pilot channel signal, the supplemental channel signal and the fundamental channel signal from the received signal RS. The demodulator device 11 demodulates the information for the supplemental channel signal from the extracted supplemental channel signal and the information for the fundamental channel signal from the extracted fundamental channel signal.
The demodulator device 11 includes path demodulator units B1, B2 and B3. The path demodulator unit B1 corresponds to a path 1; the path demodulator unit B2 corresponds to a path 2; and the path demodulator unit B3 corresponds to a path N. These path demodulator units are finger circuits.
The path demodulator unit B1 includes demodulator circuits 1, 2 and 3 that are denoted by B4, B5 and B6, respectively so as to demodulate the channel signals 1, 2 and N in the path 1. The path demodulator unit B2 includes demodulator circuits 1, 2 and 3 that are denoted by B7, B8 and B9, respectively so as to extract the channel signals 1, 2 and N in the path 2. The path demodulator unit B3 includes demodulator circuits 1, 2 and 3 that are denoted by B10, B11 and B12, respectively so as to extract the channel signals 1, 2 and N in the path 3.
For example, the channel signal 1 corresponds to the supplemental channel signal, and the channel signal 2 corresponds to the fundamental channel signal. Thus, N=2 in this example. In the path demodulator unit B1 corresponding to the path 1, the demodulator circuit B4 extracts the supplemental channel signal while the demodulator circuit B5 extracts the fundamental channel signal. Similarly, in the path demodulator unit B2 corresponding to the path 2, the demodulator circuit B7 extracts the supplemental channel signal while the demodulator circuit B8 extracts the fundamental channel signal. In the path demodulator unit B3 corresponding to the path N, the demodulator circuit 10 extracts the supplemental channel signal while the demodulator circuit 11 extracts the fundamental channel signal.
FIG. 4 illustrates a configuration of the demodulator circuit B4. Please note that FIG. 4 also illustrates a configuration of each of the demodulator circuits B5-B12 since the demodulator circuits B4-B12 have the same circuit configuration. As an example, the demodulator circuit B4 of the path demodulator unit B1 is described.
Referring to FIG. 4, a correlator 102 performs an operation for obtaining the first correlation values of the inphase component of the received signal RS input to an input end and the same code sequence as the first orthogonal code sequence used in the aforementioned modulator device 10, so as to output data having a high peak of the first correlation values as the first symbol. The correlator 102 also operates the quadrature component of the received signal RS and the same code sequence as the second orthogonal code sequence used in the aforementioned modulator device 10, so as to output data having a high peak of the operated second correlation values.
A multiplier 105 then operates the third correlation value of the first symbol and the same code sequence as the first Walsh-Code sequence xe2x80x9c+xe2x88x92+xe2x88x92. . . xe2x80x9d used in the aforementioned modulator device 10, so as to output the operated third correlation value as an inphase component of the supplemental channel signal. Also, the multiplier 105 operates the fourth correlation value of the second symbol with the second Walsh-Code sequence xe2x80x9c+xe2x88x92+xe2x88x92. . . xe2x80x9d used in the aforementioned modulator device 10, so as to output a quadrature component of the supplemental channel signal.
A correlator 103 operates, for a correlation period longer than that for the correlator 102, the in-phase component of the received signal RS input to the input end 101 and the first orthogonal code sequence, to thereby calculate the third correlation value. The correlator 103 then outputs data having a high peak value of the operated second correlation value as an in-phase component of the pilot channel signal. Also, the correlator 103 operates, for the correlation period longer than that in the correlator 102, the quadrature component of the received signal RS and the second orthogonal code sequence, to thereby calculate out the fourth correlation value. The correlator 103 then outputs data having a larger peak value of the operated third correlation value as a quadrature component of the pilot channel signal.
A propagation path estimator 104 calculates a moving average value of the inphase components of the pilot channel signal for a period corresponding to the length of N symbols. The propagation path estimator 104 outputs the calculated moving average value as an inphase component of a propagation path estimation value. In addition, the propagation path estimator 104 calculates a moving average value of the quadrature components of the pilot channel signal for the period corresponding to the length of N symbols. The obtained moving average value is output as a quadrature component of the propagation path estimation value.
The multiplier 106 multiplies the inphase component of the supplemental channel signal by that of the propagation path estimation value and also multiplies the quadrature component of the supplemental channel signal by that of the quadrature component of the propagation path estimation value. These multiplications respectively correct the amplitude component of the inphase and quadrature components of the supplemental channel signal affected by the characteristics of the propagation path. The multiplier 106 outputs the inphase and quadrature components of the supplemental channel signal that have been subjected to the above multiplications as a supplemental channel signal WS1.
The supplemental channel signal WS1 is supplied to a combining unit B14 for the channel signal 1 in a multi-path combined part B13 shown in FIG. 3.
The demodulator circuits B5-B12 work in a similar manner to that of the demodulator circuit B4. The demodulator circuit B7 outputs a supplemental channel signal WS2 in the path 2. The demodulator circuit B10 outputs a supplemental channel signal WS3 in the path N.
The demodulator circuit B5 outputs a fundamental channel signal WS4 in the path 1. The demodulator circuit B8 outputs a fundamental channel signal WS5 in the path 2. The demodulator circuit B11 outputs a fundamental channel signal WS6 in the path N.
In a case where there exists the channel signal N, the demodulator circuit B6 outputs the channel signal N WS7 in the path 1; the demodulator circuit B9 outputs the channel signal N WS8 in the path 2; and the demodulator circuit B12 outputs the channel signal N WS9 in the path N.
The combining unit B14 combines the supplemental channel signals WS1, WS2 and WS3 so as to output the combined supplemental channel signal having high reliability as a demodulation symbol CS1.
The combining unit B15 combines the fundamental channel signals WS4, WS5 and WS6 so as to output the combined fundamental channel signal having high reliability as a demodulation symbol CS2.
In the case where there exists the channel signal N, the combining unit B16 combines the channel signals N WS7, WS8 and WS9 so as to output the combined channel signal N having high reliability as a demodulation symbol CSN.
Therefore, it is an object of the present invention to provide a demodulator device and a demodulation method which overcome the above issues in the related art. More specifically, it is an object of the present invention to provide a demodulator device and a demodulation method that can demodulate transmitted information from a received signal by subjecting correlation values of the received signal and orthogonal codes to a simple add/subtraction operation, a sign inversion/non-inversion operation and accumulation. This object is achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.
According to the first aspect of the present invention, a demodulator device for demodulating a first transmitted symbol that is modulated into a first signal by spread spectrum modulation using a first code sequence and a second code sequence from a second signal including the first signal is provided. The first code sequence includes a first code series composed of a first code and a second code and a second code series composed of a third code and a fourth code, and the first code series is connected to the second code series in series. The demodulator device comprises: a first correlator operable to operate correlation values of the second signal and a third code sequence equal to the second code sequence, and add one of the adjacent ones of the correlation values to the other when the first code is equal to the second code or subtract one of the adjacent ones of the correlation values from the other when the first code is different from the second code, so as to output a first symbol; an inverter/non-inverter operable to non-inverting a sign of a value of the first symbol when the first code is equal to the third code or alternately non-inverting/inverting the sign of the value of the first symbol when the first code is different from the third code, so as to output a second symbol; and a rate adder operable to accumulate the second symbol the same number of times as a symbol rate of the first transmitted symbol to output a demodulation symbol.
The demodulator device may further includes a second correlator operable to operate correlation values of the second signal and a fourth code sequence to output first propagation path estimation values; a first propagation path estimator operable to calculate an average value of the first propagation path estimation values to output a second propagation path estimation value; and a first multiplier operable to multiply the first symbol and the second propagation path estimation value to supply a third symbol.
The demodulator device may further includes: a third correlator operable to operate correlation values of the second signal and a fifth code sequence equal to the second code sequence, and to add one of adjacent ones of the correlation values of the second signal and the fifth code sequence to the other when the first code is equal to the second code or to subtract one of the adjacent ones of the correlation values of the second signal and the fifth code sequence from the other when the first code is different from the second code, so as to output a fourth symbol; a fourth correlator operable to operate correlation values of the second signal and a sixth code sequence to output third propagation path estimation values; a second propagation path estimator operable to calculate an average value of the third propagation path estimation values to output a fourth propagation path estimation value; a second multiplier operable to multiply the fourth symbol by the fourth propagation path estimation value to output a fifth symbol; and a multi-path combiner operable to operate a value obtained by multi-path combination of the third symbol and the fifth symbol to supply a sixth symbol to the inverter/non-inverter.
In the demodulator device, the first code sequence may be a Walsh-Code sequence, and the second code sequence may be composed of a PN (Pseudorandom Noise)-Code sequence.
According to the second aspect of the present invention, a demodulation method for demodulating a first transmitted symbol that is modulated into a first signal by spread spectrum modulation using a first code sequence and a second code sequence from a second signal including the first signal is provided. The first code sequence includes a first code series composed of a first code and a second code and a second code series composed of a third code and a fourth code, and the first code series and the second code series are connected in series. The demodulation method comprises: the first step of operating correlation values of the second signal and a third code sequence equal to the second code sequence, and adding one of adjacent ones of the correlation values to the other when the first code is equal to the second code or subtracting one of the adjacent ones of the correlation values from the other when the first code is different from the second code, so as to output a first symbol; the second step of non-inverting a sign of a value of the first symbol when the first code is equal to the third symbol or alternately inverting/non-inverting the sign of the value of the first symbol when the first code is different from the third code, to output a second symbol; and the third step of accumulating the second symbol the same number of times as a symbol rate of the first transmitted symbol to output a demodulation symbol.
The demodulation method may further include: the fourth step of operating correlation values of the second signal and a fourth code sequence to output first propagation path estimation values; the fifth step of calculating an average value of the first propagation path estimation values to output a second propagation path estimation value; and the sixth step of multiplying the first symbol by the second propagation path estimation value to supply a third symbol to the second step.
The demodulation method may further include: the seventh step of operating correlation values of the second signal and a fifth code sequence equal to the second code sequence, and adding one of adjacent ones of the correlation values of the second signal and the fifth code sequence to the other when the first code is equal to the second code or subtracting one of the adjacent ones of the correlation values form the other when the first code is different from the second code, so as to output a fourth symbol; the eighth step of operating correlation values of the second signal and a sixth code sequence to output third propagation path estimation values; the ninth step of calculating an average value of the third propagation path estimation values to output a fourth propagation path estimation value; the tenth step of multiplying the fourth symbol by the fourth propagation path estimation value to output a fifth symbol; and the eleventh step of operating a value obtained by multi-path combination of the third symbol and the fifth symbol to supply a sixth symbol to the third step.
In the demodulation method, the first code sequence may be a Walsh-Code sequence, and the second code sequence may be a code sequence composed of a PN (Pseudorandom-Noise)-Code sequence.
This summary of the invention does not necessarily describe all necessary features of the present invention. The present invention may also be a sub-combination of the above described features. The above and other features and advantages of the present invention will become more apparent from the following description of embodiments taken in conjunction with the accompanying drawings.